Apparatus and method for removal of oil entrained in air



May 24, 1966 D. B. FALL ET AL PPARATUS AND METHOD FOR REMOVAL OF OILENTRAINED IN AIR 2 Sheets-Sheet 1 Filed Oct. l, 1962 May 24, 1966 D. B.PA| ET AL APPARATUS AND METHOD FOR REMOVAL OF OIL ENTRAINED IN AIR 2Sheets-Sheet 2 Filed Oct. l 1962 United States Patent O 3,252,270APPARATUS AND METHOD FOR REMOVAL F OIL ENTRAINE!) IN AIR David Il. Pall,Roslyn Estates, and Herbert L. Forman, Plainview, NX., assignors to PallCorporation, Gien Cove, NX., a corporation oi New York Filed Oct. 1,1962, Ser. No. 227,380 19 Claims. (Ci. 55-74) Compressed air is utilizedin a great many industr-ial I applications, and many types of equipmentfor compressing air are in use, such as compressors of the reciprocatingpiston type, rotary compressors, turbines, and the like. Suchcompressors are lubricated with petroleum hydrocarbon lubricants. Duringcompression, air temperature is raised, generally in the range of 400 to700 F. or

higher for air compressed by a factor of more than four in a singlestage. At these high temperatures, some of the lubricating oilvaporizes, and many of the components of the vapor react with each otherand with air to form a wide range of organic products includingoxygenated and part-ially oxygenated compounds, nitrogen compounds, andhydrocarbons in the low .to intermediate molecular Weight range. Suchvapor phase contaminants are in addition to liquid phase lubricants thatare mechanically entrained in the air.

As a result, air compressed in conventional fashion generally containsfrom about to 25 parts per m-illion parts of air by weight oflubricating oil-derived contaminants, varying from non-condensiblehydrocarbon gases to droplets of lubricant microns or more in diameter.In many industrial applications, the presence of even trace quantitiesof such contaminants -is extremely objectionable. For example, thepresence of such contaminants in air used in pneumatic instrumentcontrol systems causes orifices and moving parts to become covered withoil, thereby leading to dust collection and consequent instrumentmalfunction. Flow meters of some types will offer false data if coatedwith oil. As little as 3 parts per million of hydrocarbons entrained inair at high pressures, for example 3000 p.s.i., can form an explosivemixture. It is particularly essential that air or other inert gases usedfor compressing oxidizing agents such as -liquid oxygen, nitric acid, orhydrocarbon peroxide, be free of hydrocarbons to avoid possibility ofexplosion. Compressed air intended for human breathing, as, :forexample, in underwater diving equipment, should be free of allpotentially harmful contaminants. In chemical processes, oil incompressed air added to a reactor can introduce impurities or change thecourse of the reaction. Sewage disposal units require compressed airfree from entrained oil in order to prevent buildup of sludge.

Different approaches are in use to obtain substantially oil-freecompressed air. A compressor which does not need oil lubrication can beused, such as a liquid-packed ring type rotary compressor. This type ofcompressor, however, gives a much lower maximum pressure than a pistontype compressor. Diaphragm type and carbon ring compressors aregenerally considered to involve overly great expenditures, both ininitial cost and for maintenance.

It has been proposed to filter oil from compressed air. However, oilentrained in air is composed of a plurality of droplets having varyingsizes, ranging from a diameter of more than 25 microns down to moleculardimensions. While filtration is adequate to remove large-r sizeddroplets, droplets of the order of magnitude of labout 0.3 micron andhigher, no filter has been available which has been capable of removingsmaller sized droplets without at the same time causing an unduly largepressure drop in the air being treated. The pressurevdrop problem isparticularly noticeable when air at a pressure greater than about 25p.s.i.g. is being treated since conventional low porc size-high voidscontent filter media are generally incapable of resisting such highpressures, necessitati-ng resort to more rigid, much less porous filtermedia such as ceramic filters. Ceramic filters, while capable ofwithstanding high pressures, cause extremely high pressure drops in theair being treated. Despite this, such filters have not been capable ofremoving vaporized impurities in the air or even liquid droplets in -thesize range of 0.05 micron and smaller.

Activated carbon beds or beds of other sorbents remove entrained vaporsand droplets smaller than about 10 to 20 Angstrom units (.001 to .002micron), but have no effect on larger droplet sizes. Conventionalfilters having a sufiiciently high degree of porosity to minimizepressure drop and suitable for use in treating compressed air can removeonly droplets larger than about .3 to 3 microns in diameter, dependingupon the pore size of the filter. Hence, a combination of an activecarbon bed and a conventional filter removes droplets of 0.3 to 3microns in diameter and larger, and droplets of less than .001 to .002micron in diameter but has substantially no effect on droplets which arelarger than about .001 to .002 micron but smaller than about .3 to 3microns.

The proportion of oil droplets entrained in compressed air havingdiameters within the range of .0015 to 1.5 microns has been foundgenerally to range from 5 to 30% by weight of the total oil contententrained in the air. Accordingly, if the original -oil content of thecompressed air were 20 parts per million by weight, the use of aconventional filter plus an activated carbon bed would fail to remo-vefrom 1 to 6 parts per million of entrained oil, a residual oil contentmuch too large for many applications.

By means of the apparatus and method of this invention, substantiallyall of the oil and hydrocarbons higher than methane in molecular weightentrained in compressed air can be removed. This invention isparticularly applicable to compressed air having a pressure greater than25 p.s.i.g.

The method o f this invention comprises two essential treatment steps:passing the compressed air through a pleated high area microporousfilter element of the fibrous depth type having an average pore size ofless than 1 micron and a voids volume of at least percent and contactingthe compressed air with a sorbent capable of sorbing hydrocarbon vapors.The two steps can be carried out in either sequence. The air can befirst contacted with the sorbent and then passed through the microporousfilter element or vice versa. Each sequence has certain advantages aswill be seen from the following description. Optionally, the twoessential steps can be preceded by an additional filtration step inwhich a conventional lter is employed.

The microporous filter should have an average pore size of less than`about l micron and preferablyl an average pore size of less than about0.5 micron. Microporous filters having average pore sizes greater thanabout l micron are not satisfactory for removing oil entrained incompressed air, since they permit the passage of oil droplets which arenot ordinarily removed either by the conventional filter, if one isemployed, or by the sorbent. There is no effective lower limit on thepore size of the microporous filter, except that imposed by an excessivepressure drop of the air in passing through the filter. This, of course,depends upon the quantity of air, the thickness of the filter, and theoil content and particle size distribution thereof in the air. It hasbeen found, in practical applications, that microporous filters havingan average pore size as low as .02 micron and even lower are effective.-

It is preferred that the microporous filter element be fiexible.Flexible materials exhibit a surprisingly low tendency toward cloggingas compared to unfiexible filters, such as rigid metallic filters. Thismay be due to a tendency of the microporous filter to fiex under theforce of the compressed air, thus expelling ultrafine droplets thatmight otherwise tend to clog the filter.

The depth or thickness of the microporous fibrous filter is notcritical. A thick filter operates efiiciently, but it should not createan undue pressure drop.

A preferred microporous filter for use in this invention is made of aporous base, such as paper, having relatively large pores, within or onthe surface of which is deposited particulate material in an amount todiminish the average diameter thereof to less than l micron whileretaining a voids volume in the microporous portion in excess of 75%, asdisclosed in copendin-g applications Serial No. 98,595, filed March 27,1961, and Serial No. 215,151 filed August 6, 1962, the disclosures ofwhich are herein incorporated by reference. The particulate material,which can be in the form, for example, of fibers or fine structuredgranules, is suspended in a fiuid and deposited therefrom upon thesurface of 'the porous base material. The particulate material can allbe of the same size and type, or of two or more sizes and types, allsuspended in the fluid system. The desired reduction in pore diameter ofthe base is obtained-by varying the size and amount of the particulatematerial deposited, blending different sizes at different points, ifdesired. A particularly preferred microporous filter is one of the typedescribed in application Serial No. 215,151, filed August 6, 1962, whichcomprises a porous base having superimposed thereon and adherent theretoa microporous layer comprising a fibrous material of which a proportionof fibers extend outwardly from the porous base at an angle greater than30, the microporous layer having an average pore diameter of less than 1micron and a voids volume of at least 75 percent. The 'fiber spacing andangular disposition to the base throughout the, entire microporous layeris noted by cross-sectional examination, upon sufiicient magnificationthrough an optical or electron microscope. The angular disposition ofthe fibers is in large measure responsible for the high voids volume andlow pore size characteristic of the microporous filters preferred foruse in this invention.

When fibers are laid down on a base in a conventional manner, they tendto lie almost entirely in planes parallel to the base. Such conventionalfiber layers can :be permeable to fluids, and can have a fairly low poresize, but they are universally characterized by low voids volumes, sothat their use as filter media is not feasible. The proportion ofangularly extending fibers, and the wide spacing of the fibers, both ofwhich are characteristic of the preferred filters, serve to holdthe'fibers in the layer generally farther from the base, therebyincreasing substantially the voids volume of the microporous layer.Since the fibers are relatively small, the interstices between them attheir lpoints of crossing will be very small, but since they are heldfarther apart, their interstices are fewer in number per unit volume. Inconsequence, the preferred filters have a very small pore size, and ahigh voids volume.

In order to insure good adhesion between the deposited layer and thebase, an anchoring layer can be applied to the base prior to theapplication of the main layer. Such an anchoring layer is applied bytreating the base with an anchoring dispersion comprising `a liquid orliquefiable binding agent and a particulate fibrous material which iswetted by the binding agent.

Fibrous material is preferred as the particulate material to bedeposited because of its versatility, and because of the greater ease ofdeposition as a film. A great variety of diameters of fibers areavailable, thus making it possible to achieve a very large assortment ofmixtures of different diameter fibers for making fibrous material of anyporosity, and such fibers can be made of any length, so as to takeadvantage of the greater cohesiveness of a layer of long'fibers, ascompared to granular material layers. Generally, fibers having diametersof 2 microns or less are preferred. Typical fibrous materials includeglass, asbestos, potassium titanate, aluminum silicate, mineral wool,regenerated cellulose, polystyrene, polyvinyl chloride, polyvinylidenechloride, polyacrylonitrile, polyethylene, polypropylene, rubber,polymers of terephthalic acid and ethylene glycol, polyamides, caseinfibers, zein fibers, cellulose acetate, viscose rayon, hemp, jute,linen, cotton, silk, wool, mohair, paper, and metallic fibers such asiron, copper, aluminum, stainless steel, brass, Monel, silver, andtitanium.

Nonfibrous particulate materials can be used in admixture with fibrousmaterials. However, in order to achieve the requisite microporosity andvoids volume, it is essential to employ at least one part by weight offibrous material for every three parts of nonfibrous materials Whennonfibrous particles are employed, they should have an average diameternot exceeding 10 microns. Those nonfibrous materials containing a fineinternal structure or porosity are preferred.

Typical nonfibrous particulate materials are diatomaceous earth,magnesia, silica, talc, silica gel, alumina, quartz, carbon, activatedcarbon, clays, synthetic resins and cellulose derivatives, such aspolyethylene, polyvinyl` chloride, polystyrene, polypropylene,ureaformaldehyde, phenol-formaldehyde, polytetrafiuoroethylene,polytrifiuorochloroethylene, polymers of terephthalic acid and ethyleneglycol, polyacrylonitrile, ethyl cellulose, polyamides, and celluloseacetate-propionate, and metal particles such as aluminum, silver,platinum, iron, copper, nickel, chrominum and titanium and metal alloysof all kinds, such as Monel, brass, stainless steel, bronze, lnconel,cupronickel, Hastelloy, beryllium, andpcopper. Combinations ofdiatomaceous earth and glass fibers give excellent results.

Any porous material whose pores extend from surface to surface can beused as a base upon or within which the microporous layer is deposited.One or several layers of the same or varying porosity can be employedand can be composed of cellulose or other fibers. Paper, which can, ifdesired, be resin impregnated, is a preferred base material since ityields an effective, versatile and inexpensive microporoushuid-permeable medium. Where desired, other base materials can be used,such as porous sintered powders or forms of metals and of natural orsynthetic plastic materials, such as aluminum, and synthetic resins andcellulose derivatives, in the form of spongy layers of any desiredthickness, such as polyurethane (see Patent No. 2,961,710), polyvinylchloride, polyethylene and polypropylene sponges and foams, woven wireproducts, sintered or unsintered, textile fabrics and woven and nonwovenfibrous layers of all kinds, such as felts, mats and bats, made of brousmaterials of any `of the types listed below in connection with theparticulate material. The porous base material will have an average porediameter of not less than about 2.5 microns. Such materials will ofcourse have pores as large as 2O to 25 microns, or more.

The fiuid medium used for the dispersion is preferably inert to theparticulate material and the base material. It should not dissolve asubstantial amount thereof, although if the fiuid is reused, the factthat some material is in solution is not a disadvantage, since asaturated solution is quickly formed ab initio. The fluid should bevolatile at a reasonably elevated temperature below the melting point ofthe material to facilitate removal after the dispersion is deposited.However, nonvolatile fiuids may be desirable under certain conditions,and those can be removed, by washing out with a volatile solvent that isa solvent for the fiuid but not for the particulate material. i

Typical fluids are water, alcohols, polyalkylene glycols, such aspolyethylene glycols, poly 1,2-propylene glycols, and mono and di alkylethers thereof, such as the methyl, ethyl, butyl and propyl mono and diethers, dialkyl esters of aliphatic dicarboxylic acids, such as,di-2-ethylhexyl adipate and glutarate, mineral lubricating oils,hydraulic fluids, vegetable oils, and hydrocarbon solvents such asxylene and petroleum ether, silicone fiuids, chloro, bromo and fiuorohydrocarbons, such as the Freons. Since the final product is permeableto any liquid, depending upon the choice of particulate material,obviously a w-ide selection of fluids is available, and such would beknown to one skilled in this art.

The sorbent with which the compressed air is to be contacted can be ofany type known to the art for use in sorbing hydrocarbon contaminantsfrom air. The term sorption is inclusive of the processes known asadsorption and absorption, the distinction being that molecules are saidto be absorbed When they enter the inside of a solid material, i.e., theabsorbent, and are said to be adsorbed when the molecules remainattached to the surface of the solid adsorbent.

Activated carbon is the preferred sorbent for use in this invention,since it is capable of efficiently sorbing hydrocarbon contaminants suchas oil from air without being affected by an moisture contained in theair. Activated carbon can be employed alone, or it can be catalyzed withfrom about 0.2 to 5% of palladium, platinum, rhodium, cesium, rubidiumor cuprous oxide. Activated carbon is also increased in activity by theaddition of from about 5 to 20% by weight of the mixture of the oxidesof copper, cobalt, manganese and silver, commercially known as HopcoliteA number of other materials also have activity as sorbents, such as, forexample, various crystalline substances and such other materials aschabicite, pumice, either alone or catalyzed with up to nickel, silicagel, chromic oxide gel, lithopone, powdered porous glass, glass wool,activated alumina, quartz crystals, fullers earth, Cecil soil, Barnessoil and glaucosil, which is useful particularly in removing oil fromair of low water vapor content.

It is preferable that the sorbent employed have a large surface areaexposed to the passage of compressed air. Accordingly, it is preferredthat the solid sorbents be in particulate form, and not be compressed.

The sorbent should be located within a confined area which is permeableto the free passage of the compressed air, so that the air is passedthrough or over the sorbent. For example, the sorbent can be locatedwithin a chamber in the path of the compressed air. At least two wallsof the chamber are comprised of a porous material which has pores largeenough so as not to restrict the passage of compressed air, but smallenough to prevent the loss and consequent contamination of the air byparticles of the sorbent.

The quantity of sorbent required is proportional to the volume of air tobe treated per unit time, and the amount of oil entrained. The greaterthe volume of air containing a given oil content, per unit time, thegreater will be the amount of sorbent necessary to operate effectively.For most applications, the quantity of sorbent ernployed should be atleast grams per cubic foot of air passing through the apparatus perminute, calculated on the basis of standard temperature and pressure.

A preliminary filtration using a conventional filter is frequently,albeit not necessarily, desirable. Such preliminary filtration, whichcan be accomplished with any conventional filter media, preferablyhaving a pore size of between 25 and 100 microns to avoid any unduepressure drops, serves to remove any very large oil droplets which mighttend to clog the pores of the sorbent or the microporous filter.Exemplary of such conventional filters are filter paper and perforatedmetal sheets. p The microporous filter used in this invention ispreferably in pleated or corrugated form to expose maximum surface areto the passage of compressed air within the limits of a confined unit.Where the filter employed is not in corrugated form but instead is ofthe smooth cylindrical type, even if made of the preferred fibrous depthvariety of filter, a greater resistance to the passage of air will bedeveloped unless a much larger size filter is employed, thus making theunit very large and inconvenient for use. Where, of course, size orspace limitations are not a problem or where only negligible quantitiesof entrained oil are to be removed, smooth filters can be resorted to ifthe pleated or corrugated variety is notv available. The length of thecorrugated filter element Ias well as the depth and number of thecorrugations will depend upon actual service requirements. Generally,elements having a length of from 2 to 30 inches, internal diameters(measured at the base of the corrugations) of from 0.5 to l0 inches,external diameters of from 0.8 to 25 inches and from about 10 to 100pleats give good results. are useful under particular operatingconditions.

In operation, the method of this invention can be carried out byemploying a separate filter unit in which the filter element is made ofa microporous flexible material as above described and a porous canistercontaining a quantity of the sorbent material such as activatedcharcoal. These two separate units can be placed at any point downstreamof the air compressor and upstream of the ultimate end usefor the vairand the results of this invention can thereby be achieved. Optionally,the initial conventional filtration step can also be employed at 4anypoint prior to either of the other operations.

A preferred oil removal unit of this invention is shown in FIGURE l, andis composed of three concentric layers, the outer layer being aperforated metal cylinder, the

intermediate layer being a sorbent, .such as activated carbon, and theinner layer being a microporous fiexible filter. This treating unit canbe placed downstream of a compressor and the air forced to pass through,in sequence, firstly the perforated' metal cylinder, secondly thesorbent and thirdly the microporous filter, the air exiting from thecomposite unit in a condition substantially free from entrained oil, andsuitable for applications in which the presence of even trace amounts ofoil would be undesirable.

An alternative type of oil removal unit of this invention is shown inFIGURE 3, and can be connected to a compressed air line between any twopoints thereof, so that the compressed air passes in sequence throughthe microporous flexible filter and the sorbent, but in either order, asdesired.

Further details of the apparatus of this invention can be had byreference to the drawings, in which-- FIGURE 1 illustrates a cartridgefor an oil removal unit comprising two concentric filter layers and onesorbent layer; A

FIGURE 2 is a cross `section of the cartridge of FIG- URE l, takenthrough the line 2 2 of FIGURE 1; and

FIGURE 3 illustrates an oil removal unit for connection to a compressedair line so that air passes, in sequence, through a microporous flexiblefilter and then through a sorbent.

The oil removal cartridge of FIGURE 1 is in the form of a hollowcylindrical shell 1 of a perforated metal, having relatively large holesof an average diameter of 0.025 inch. The open ends are closed off bynonporous outer end caps 2 and 3 having central apertures 4 and 5opening into the interior 6 of a perforated steel core 7 held byinturned portions S and 9 of the inner end caps 10 and 11. The inner endcaps Y10 and 11 in turn hold However, elements having differentdimensionsv the ends of a concentric axially corrugated cylinderl 12 ofa microporous flexible fibrous depth type filter made in accordance withthe procedure of applicationSerial No. 215,151 filed August 6, 1962, andhaving an average pore size of less than 1 micron, a voids volume ofabout 90%, an internal diameter of about 1 inch, and external diameterof about 11/2 inches and about 30 corrugations. Disposed in the spaceintermediate the inner cylinder 12 and the outer cylinder 1 is a sorbentlayer 13, made up of approximately 350 grams of particulate activatedcarbon having an average particle size of 4 t-o 6 mesh, held in place bythe cylinders and outer end caps 2 and `3. Flat gaskets 14 and 15 arefitted in grooves in the end caps 2 and 3, so as to seal the oil removalcartridge in an oil removal unit, and prevent intermingling of treatedair with untreated air.

In operation, the cartridge and oil removal unit are put, for example,downstream of the compressor in a compressedA yair system, and aircontaining entrained oil and other hydrocarbon impurities is caused toenter the cartridge through perforated cylinder 1 which serves as apreliminary filter. The air then passes through sorbent 13 and themicroporous lter 12, during which passage entrained oil is removed, sothat oil-free air enters interior passage 6. Interior passage 6 isconnected to the feed of oil-free compressed air. The apparatusillustrated in FIGURES l and 2 was found to be capable of removing oilfrom compressed air at air fiow rates of up to 15 cubic feet per minuteand pressures of up 75 p.s.i.g.

The oil removal unit shown in FIGURE 3 is connected at each end to acompressed air line 20. Oil-entrained air enters the unit at inlet 21,and emerges oil-free at outlet 22.

The unit is composed of two parts, designated-A and B, each comprising abowl-supporting head, 24 and 25, respectively.

The head 24 comprises an inlet 26 and a concentric outlet 27 openinginto the bowl 28 and communicating, respectively, with the outside andinside of a plurality, in this case, three, of oil-removal cartridges29. However, one cartridge may be used, or more than three, depending onthe system requirements. Each cartridge is composed of an outer shell 30of a corrugated microporous depth type filter of the type used in theFIG- URE 1 apparatus, having an average pore size of less than 1 micron.The open ends of these shells are closed off by end caps 31 havingcentral apertures opening into the central passage 32 of a perforatedmetal core 33, of plated or stainless steel. Beneath each end capadjacent the aperture and webbed'thereto for support is a V-shaped innercap 34 which engages a matching connector 35 to communicate the centralpassage 32 of one cartridge with the next adjacent cartridge. The O-ringgaskets 36 prevent leakage between the cartridges 29.

The bottommost cartridge 29 receives in its adjustor 34 a cap 38 whichis biased by spring 39 upwardly, to hold the cartridge assembly firmlyagainst the projecting end of outlet 27. Leakage is preven-ted at bothpoints by gaskets 36. Oil separated by the cartridge collects at thebottom of the bowl 28, and is removed via outlet 40.

The bowl 28 is removably attached to the head 24 by clamps 41, whichengage the upper lip 42 of the bowl and hold it firmly against thecorresponding lip 43 of the head. Leakage at the point therebetween isprevented by gasket 44.

The second unit is attached to head 25, which has an inlet 50 and anoutlet 51 opening into bowl 52 on the outside and inside, respectively,of cartridge 53. The cartridge is composed of a perforated metalcylinder 54 of plated steel or stainless steel, the open ends of whichare closed off by end caps 55, each of which has a central aperture.Beneath each cap, adjacent the aperture and welded thereto for support,is a V-shaped inner cap 56, which holds the ends of a corrugated paperfilter shell 57, the interior of which is provided with a supportingspring 58. The space intermediate the shell 57 and cylinder 54 is filledwith a sorbent 59 such as activated carbon The interior of shell 57 isopen, the central passage 60 thereby defined communicating directly withoutlet 51.

The bottom of cartridge 53 receives in the aperture of the end cap a cap61 which is biased by spring 62 upwardly to hold the cartridge firmlyagainst the projecting end of outlet 51. Leakage is prevented at bothpoints by gaskets 63.

The bowl52 is removably attached to head 25 in ex- -actly the samemanner as bowl 28.

In operation, the oil removal unit of FIGURE 3 is connected to acompressor, from which oil-entrained air enters inlet 26, filter bowl28, one of cartridges 29, through filter shell 30 into passage 32. Oilseparated by the filter at the surface of the cartridge drops into thesump of the bowl, and is removed at 40 from time to time.

Air still containing oil droplets too fine to be removed by filter 30leaves the bowl 28 via outlet 27, and enters the second unit at inlet50, passing into bowl 52, and then through the sorbent S9 and paperfilter 57 into passage 60. Now, the air is oil-free, and returns to theline 20 through outlet 51.

It will be readily understood that if desired, the apparatus can beconstructed so as to have the air contact the sorbent prior tocontacting the microporous filter or vice versa.

We claim:

1. A process for separating hydrocarbon vapors and droplets fromcompressed air which comprises the steps, taken in any order, of (1)passing the air over a sorbent for hydrocarbons and (2) passing the airthrough a microporous fibrous depth filter having an average pore sizeof less than one micron and a voids volume of at least 2. A process inaccordance with claim 1 in which the order of steps is such that the airis first passed over the sorbent and then passed through the microporousfilter.

3. A process in accordance with claim 1 wherein the order of steps issuch that the air is first passed through' the microporous filter andthen is passed over the sorbent.

4. A process in accordance with claim 1 wherein the compressed air issubjected to a preliminary filtration by passing the air through afilter having a pore size of between about 25 and about 100 microns.

5. Apparatus for separating hydrocarbon vapors and droplets fromcompressed air comprising, in combination, a housing having an inlet andan outlet for fiow of cornpressed air therethrough, and disposed acrossthe line of air flow between the inlet and outlet so that all air flowstherethrough, a microporous fibrous depth type filter having an averagepore size of less than one micron and a voids volume of at least 75%,and a bed of particulate sorbent capable of sorbing hydrocarbons.

6. Apparatus in accordance with claim 5 wherein the microporous filterand sorbent are so arranged in the line of air flow that the filter iscontacted first by the compressed air.

7. Apparatus in accordance with claim 5 wherein the microporous filterand sorbent are so arranged in the line of air flow that the sorbent iscontacted first by the compressed air.

8. Apparatus in accordance with claim 5 including, first in the line offluid fiow, a filter having an average pore size of between about 25 andabout 100 microns.

9. Apparatus in accordance with claim 5 wherein the microporous filtericomprises a porous base having superimposed thereon and adherentthereto a microporous layer comprising a fibrous material.

10. Apparatus in accordance with claim 5 wherein the microporous filterIis in corrugated form.

11. Apparatus in accordance with claim 5 wherein the microporous lilterand the sorbent bed are disposed concentrically within the housing.

12. Apparatus in accordance with claim wherein the sorbent is activatedcarbon. v

13. Apparatus for removing hydrocarbon vapors and droplets fromcompressed air comprising, in combination, a lcylindrical cannisterhaving a side wall provided with openings for passage therethrough ofcompressed air and having at least one open end closed by an end caphaving a passage therethrough for ow of compressed air, a microporoustubular fibrous depth lter having an average pore size less than onemicron and a voids volume of at least 75% disposed within thecylindrical cannister, a tubular core support disposed concentricallyand internally of the microporous lter, and a layer of particulatesorbent disposed between the core and the container side wall on oneside of the microporous tubular lter in a manner such that compressedair entering the container must pass through the sorbent layer and themicroporous lter before emerging from the container.

14. Apparatus in accordance with claim 13 in which the microporous lteris in corrugated tubular form.

15. Apparatus in accordance with claim 13 wherein the sorbent layer isdisposed internally of the lter.

16. Apparatus in accordance with claim 13 wherein the sorbent layer isdisposed externally of the lter.

17. Apparat-us in accordance with claim 13 wherein the microporousfilter comprises a porous base having superimposed lthereon and adherentthereto a microporous layer comprising a brous material.

18. Apparatus for removing hydrocarbon vapors and droplets fromcompressed air comprising, in combination, a head having air inlet andair outlet passages therethrough, a bowl attached to the head in amanner to receive air from the air inlet and to deliver air to the airoutlet, and disposed in the bowl across the line of air ow from theinlet to the outlet a tubular microporous depth type lter having anaverage pore size -of less lthan one micron and a voids volume of atleast and a layer of sorbent for hydrocarbon vapors and droplets.

19. Apparatus in accordance with claim 18 wherein lthe microporous ltercomprises a paper layer having relatively large pores and havingdeposited thereon a layer of fibrous material in an amount to reduce theaverage pore diameter thereof to less-than one micron.

References Cited by the Examiner UNITED STATES PATENTS 2,404,468 7/1946Vokes et al. 55-387 2,537,992 1/1951 Gross et al 55-316 X 2,593,1324/1952 Gannon 55-387 2,669,318 2/1954 Briggs 55--387 2,698,061 12/1954Jaubert 55-316 2,826,265 3/1958 Woody 55--523 2,951,551 9/1960 West55-316 3,064,819 11/1962 Jones 55387 X 3,084,427 4/196'3 Holcomb 210-496X REUBEN FRIEDMAN, Primary Examiner.

1. A PROCESS FOR SEPARATING HYDROCARBON VAPORS AND DROPLETS FROMCOMPRESSED AIR WHICH COMPRISES THE STEPS, TAKEN IN ANY ORDER, OF (1)PASSING THE AIR OVER A SORBENT FOR HYDROCARBONS AND (2) PASSING THE AIRTHROUGH A MICROPOROUS FIBROUS DEPTH FILTER HAVING AN AVERAGE PORE